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RUMINATION                                    281

Iii the upper jaw, and very usually there are none. As a
general rule the third and fourth metacarpals and metatarsals
become united to form a cannon bone. To this there is but one
exception, the African Hyomoschu-s. Moreover, the second and
fifth digits are nearly always rudimentary, and may practically
disappear altogether. Here again the Tragululae are an excep-
tion. The Jtumiiiantia are so-called on account of the fact that
they " ruminate/* that is, after the food has been rapidly

FIG. 146.—Stomafh. of Ruminant opened to show the internal structure,     a, Oesophagus ;
li,   rumen. ;   c,   reticttlum. ;   df,   psalterium ;   e,   at-omasum j fy   duodenum.     (After
Flower and Lydekker.)
swallowed, it is forced "back up the gullet and more thoroughly
masticated. Associated with this is a complex stomach, which
is divided into several compartments. This stomach has at least
three compartments, as in the Tragulidae ; but it has -usually four.
Its characters are illustrated in Fig. 146. The majority of the
Selenodontia possess horns, which are partly formed of solid
protuberances of the frontal bones. In the Giraffe they are
somewhat different.
This group may be divided into—A, TRAGULINA, Chevro-
tains ; B. TYLOPODA, Camels, Lamas ; and G. PECORA, Deer, Ante-
lopes, Oxen, Giraffes, Goats, Sheep.
As the Tragulina are undoubtedly the xaosfc ancient of the
Selenodontia it will be logical to commence with an account
of them.